Phased array laser source

ABSTRACT

This invention is directed to an electronically scanned laser array. It utilizes a phase-locking laser, an array of variable phase shifters, an array of semiconductor lasers and a control computer. The output of the phase-locking laser is optically coupled, by means of reflective or transmission optics, to the phase shifters which are controlled in a predetermined pattern by the computer. The phase shifters are optically coupled to the array and cause uniform shifts in the phase front of the arrayed lasers to provide a scanning effect of the output beam.

United States Patent 51 3,691,483 Klein 1 Sept. 12, 1972 [54] PHASEDARRAY LASER SOURCE 3,504,302 3/1970 Fenner ..332/7.51 72 Inventor; AaronDavid Klein 2 1 C 3,331,651 7/1967 Sterzer ..350/96 gong! kgggjwggggmgzMd 20 52 3,284,799 11/1966 Ross ..343/6 [22] Filed: 1970 PrimaryExaminer-Benjamin A. Borchelt [21] Appl. No.: 14,823 AssistantExaminer-N. Moskowitz Attorney-R. S. Sciascia and Thomas 0. Watson, Jr.

[52] US. Cl. ..332/7.51, 331/945, 350/160 51 Int. Cl ..H0ls 3/02, 1104b9/00 [57] ABSTRACT [58] Field of Search ..332/7.5l; 330/43; 343/778;This invention is directed to an electronically scanned 331/945;350/160, 285 laser array. It utilizes a phase-locking laser, an array ofvariable phase shifters, an array of semiconductor l ces Cited lasersand a control computer. The output of the UNITED STATES PATENTSphase-locking laser is optically coupled, by means of reflective ortransmission optics, to the phase shifters 3,590,248 6/1971 Chatterton.;..250/199 which are controlled in a predetermined pattern by 3,517,3376/ 1970 Shah ..350/ 160 the om uter, The phase shifters are opticallycoupled 3,515,458 6/1970 Korpel ..350/ 160 V t th ay and gauge uniformshifts in the phase Korpcl f nt of the arrayed lasers to provide acanning efiect 3,519,953 7/1970 Gamblm et a1. ..33-1/94.5 f the outputbeam 3,484,713 12/1969 Fennel ..331/94.5 3,465,159 9/1969 Stern..330/4.3 5 Claims, 3 Drawing Figures DRIVER 26 COMPUTER SHIFTER 3; 3/

l l l j /4 m PHASE, E WR g l /3. E 'fi 23 /5 g 5 PHASE N 5 sniff?" q EHAsE SHIFTER i l.. l I 25 I7 M SHIFTER STATEMENT OF GOVERNMENT INTERESTThe invention described herein may be manufactured and used by or forthe Government of the United States of America for governmental purposeswithout the payment of any royalties thereon or therefor.

BACKGROUND OF THE INVENTION This invention relates to laser scanningand, more particularly, it relates to electronic scanning of thecoherent light output of an array of semiconductor lasers. The inventionhas application in optical radar systems and holography as well as inaddresses for optical storage systems.

Laser scanning in the prior art was achieved mechanically by rotatingmirrors and by the use of opto-acoustic crystals which utilizeultrasonic waves to bend the laser beam. The scanning in these methods,

however, is slow and they are not readily adaptable to automaticcontrol.

Prior art electronic laser scanning systemsonly use a single laser. Thelaser beam is seperated' into a plurality of portions by fiber opticsand a phase-shift is applied to each portion. The plurality of beamportions are then converged by fiber optics. This system, however, has anumber of disadvantages. The laser employed must be a high power outputlaser, or else the phase shifted output will be low power and notreadily utilizable. The optical phase shifters employed must thus becapable of withstanding a high power beam. Further, placing the opticalphase shifters in a position where they operate on the beam just priorto utilization is undesirable. Phase shifters so placed will causescattering, distortion and feedback into the laser generating the beam.

SUMMARY OF THE INVENTION The inventive system represents a substantialimprovement over the prior art. It causes the electronic scanning of thecoherent light output of an array of lasers without subjecting theoptical phase shifters to a high power beam while producing a morehighly coherent beam. The inventive system is also more compact andefficient than any of the prior art systems.

The inventive system utilizes a master optical maser or laser oscillatorto provide phase-locking light beams as inputs for an array ofsemiconductor lasers. The master laser beam is fed to an array ofoptical phase shifters by means of mirrors or lenses. Each optical phaseshifter provides a predetermined phase shift to its received beam andpasses it one to its respective semiconductor laser in the array. Theoptical phase shifters are automatically controlled by a computer andshift the relative phase of their respective incoming beams. This phaseshifting is controlled to cause the laser array output to sweep througha given angle.

By using an array of semiconductor lasers, the system overcomes thepower and distortion problems involved when a single laser is used. Thesemiconductor lasers are also extremely efficient and compact. Inaddition, the phase shift effect can be achieved in the semiconductorlaser structure itself, thereby eliminating the space taken by externalphase shifters.

OBJECTS OF THE INVENTION It is therefore an object of the presentinvention to provide a new and improved apparatus for electronicallyscanning a laser beam.

It is a further object of the present invention to provide an apparatusfor scanning a laser beam which is highly efiicient and compact.

It is a still further object of the present invention to provide anapparatus for electronically scanning a laser beam in which the lasingand phase shifting occur within the same structure.

Other objects, advantages and novel features of the invention willbecome apparent from the following detailed description of the inventionwhen considered in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic of the inventivesystem; and

FIG. 2 shows a phase shift applied to the phase shifter array; and

FIG. 3 illustrates schematically a semiconductor laser that willaccomplish both phase shifting and coherent light generation.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to FIG. 1, theinventive system utilizes a master optical maser or laser 1 1 as a lightsource. The output of laser 11 is distributed to the optical phase shiftarray 21-25, which may be planar or non-planar, by means of reflectiveoptics such as mirrors, or coherent transmission optics such as lensesor coherent light tubes. A fiber optics cluster may also be used butwith poorer results. Box 12 of FIG. 1 represents either a reflectiveoptics or coherent transmission optics system, both of which are knownin the art, to distribute the beam generated by laser 1 1.

Electro-optical phase shifters 21-25 are automatically controlled by acomputer 26. The phase shifters may be any of the well known types suchas a Kerr or Pockel cell. The phase shifted beams are fed into thesemiconductor laser array 13-17 which is in close proximity to the phaseshifter array.

All of the lasers utilized are of the semiconductor type and althoughFIG. 1 shows junction lasers, it should be noted that bulk-effect,electronic beam or any similar type of semiconductor laser may beutilized. Semiconductor lasers were chosen because they are highlyefficient and compact.

All of the lasers are controlled by a driving circuit 18. The drivingcircuit can either provide pulses or a con tinuous excitation.

In optimum space applications the phase shift can be accomplished byusing the laser semiconductor structure shown in FIG. 3. By utilizingdual function semiconductor laser 34, which is well known in the art, inthe manner shown, phase shift and coherent light generation isaccomplished in the same package. The semiconductor laser 34 which maybe made of galium arsenide is divided into two sections by notch 35. Byvarying the reverse bias 36 of one side of such a semiconductor laservariation of the phase shift of an incoming signal is accomplished.Varying the forward bias 37 of the other side results in amplificationof the incoming signal or oscillation at the frequency of the incomingsignal.

In operation, the. driver 18, when turned on,

7 generally applies a continuous current to lasers 11 and 13 to 17. Theoutput of the master laser 11 is optically coupled through opticaldistributer 12 to the phase shifter array 21-25. which is controlled bycomputer 26. FIG. 2 shows the phasefront 32 obtained at the outputs of21 to 25 when a l80 relative phase shift is applied by the phaseshifters to wavefront 31. The sinusoidal outputs of the phase shiftersare designated by the numerals 21' to 25'.

The computer is programmed to maintain a constant relative phasedifference between the outputs of adjacent phase shifters. The computergenerally is operative to apply a signal to the phase shifters whichwill vary this relative phase difference in increasing steps from aminimum to a maximum which is dictated by the size and number of phaseshifters utilized.

As the relative phase of each phase shifter is shifted, the beam willassume a deflected position as a result of the cancellation and addingof the plurality of differently phased light beams. By varying therelative phases in incremental sequential steps, a scanning of theprojected light beam is accomplished. In view of practicalconsiderations such as the size and number of phase shifters, a scanningangle of l is possible in the present state of the equipment art.

The phase front 32 is imposed on laser array 13-17. The laser array13-17 is located in very close proximity to the phase shifter array21-25 so that no interaction of the individual light beams occurs untilthey leave the laser array 13-17. By utilizing dual functionsemiconductor laser 34 of FIG. 3, the location of the phase shifterarray relative to the laser array is inherently solved.

Semiconductor lasers 13-17 may be pumped by driver 18 below their lasingthreshold so that the power of the beam generated by laser 11 will besufficient, in combination with the pumping energy supplied by driver18, to cause the respective lasers within the array to generate anamplified light beam. This manner of operation is analogous to thefunction of an amplifier. The beam outputs of the respectivesemiconductor lasers in the array will be locked into the phase of theinput signal because main laser 11 is of the same signal characteristicsas the individual lasers of the array. A theoretical explanation for theoccurrence of this observed phenomena is not available at this time.However, its occurrence is known in the art.

If the individual lasers within the array 13-17 are pumped above thelasing threshold by driver 18, they will generate coherent light in anoscillatory manner, in the same manner as main laser 11. When the lightbeam from the phase shifter array 21-25 impinges on the respectivelasers within the array, the power of the output light beam from eachrespective laser within the array will not change greatly. However, theoutput beam of each respective laser will be phase locked into the phaseof the input to the laser. Prior to the beam from the phase shifterarray 21-25 impinging on the respective lasers in the array, each laserwithin the array would be oscillating with a nondeterminedindiscriminate relative hase.

Upon leaving la er array 13-17, the individual beams with theircontrolled relative phase shifts interact to create a beam that isdeflected in a predetermined direction. By sequentially changing therelative phase relationship of the array via the computer 26 and thephase shifter array 21-25, the beam is scanned.

Thus, it is seen that a new and improved apparatus for electronicallyscanning a laser beam has been provided. The inventive system utilizesan array of semiconductor lasers to provide a high powered output in acompact and efficient manner.

Obviously many modifications and variations of the present invention arepossible in the light of the above teachings.

What is claimed is: 1. An apparatus for electronically scanning a beamof coherent light comprising:

a driver means; a first source of coherent light pumped by said drivermeans; 7

an array of electro-optic phase-shifting means having an optical inputand output, and operative to produce, at its optical output, a beam oflight which is phase shifted from a beam of light impinging on itsoptical input;

optical coupling means for optically coupling the output of said firstsource to the input of each of said phase-shifting means in the array;an array of second sources of coherent light pumped by said driver meansand individually coupled to the corresponding optical output of saidarray of phase shifting means to amplify the received light;

each of said phase-shifting means and its corresponding second source ofcoherent light are embodied within a single dual function laser means,and a plurality of the dual function laser means form said array;

phase locking means for holding the first and second sources of coherentlight phase locked;

automatic control means connected to said electrooptic phase shiftingmeans for varying the phase shift applied by said phase-shifting means.

2. The apparatus of claim 1 wherein said phase locking means comprisessaid driving means pumping said first and second sources of coherentlight simultaneously.

3. The apparatus of claim 1 wherein said first and second sources ofcoherent light comprises semiconductor lasers.

4. The apparatus of claim 1 wherein said dual function laser meanscomprises a semiconductor laser structured to accept electrical phaseshift signals and pumping signals along with light signals.

5. The apparatus of claim 4 wherein said automatic control means variesthe signals applied to said plurality of dual function laser means tosystematically vary the relative phase shift applied to the output ofsaid first source of coherent light whereby scanning of the output ofsaid array of dual function laser means occurs.

1. An apparatus for electronically scanning a beam of coherent lightcomprising: a driver means; a first source of coherent light pumped bysaid driver means; an array of electro-optic phase-shifting means havingan optical input and output, and operative to produce, at its opticaloutput, a beam of light which is phase shifted from a beam of lightimpinging on its optical input; optical coupling means for opticallycoupling the output of said first source to thE input of each of saidphase-shifting means in the array; an array of second sources ofcoherent light pumped by said driver means and individually coupled tothe corresponding optical output of said array of phase shifting meansto amplify the received light; each of said phase-shifting means and itscorresponding second source of coherent light are embodied within asingle dual function laser means, and a plurality of the dual functionlaser means form said array; phase locking means for holding the firstand second sources of coherent light phase locked; automatic controlmeans connected to said electro-optic phase shifting means for varyingthe phase shift applied by said phase-shifting means.
 2. The apparatusof claim 1 wherein said phase locking means comprises said driving meanspumping said first and second sources of coherent light simultaneously.3. The apparatus of claim 1 wherein said first and second sources ofcoherent light comprises semiconductor lasers.
 4. The apparatus of claim1 wherein said dual function laser means comprises a semiconductor laserstructured to accept electrical phase shift signals and pumping signalsalong with light signals.
 5. The apparatus of claim 4 wherein saidautomatic control means varies the signals applied to said plurality ofdual function laser means to systematically vary the relative phaseshift applied to the output of said first source of coherent lightwhereby scanning of the output of said array of dual function lasermeans occurs.